1. Field of the Invention
The present invention relates to an optical head for use in a device for recording or reproducing optical information, by irradiating a disk-shaped recording medium (hereinafter referred to as a disk) with a light beam.
2. Prior Art
Referring to FIG. 1, an example of a conventional optical head will be illustrated. As illustrated, a light beam emitted from an optical source 1 is directed toward a polarized beam splitter 3 and a .lambda./4 plate 4 via a coupling lens 2, diverted 90.degree. by an optical path converting prism mirror 5, and focused onto a recording surface 7a of a disk 7 through an objective lens 6. The light means reflected back from the recording surface 7a is reflected on the reflecting plane of the polarized beam splitter 3, and detected by an optical detector 8.
The follow-up control of the focusing position and tracking position of the optical head arranged as described above is performed by the use of a focusing actuator 9 and a tracking actuator 10. To be concrete, the follow-up control is conventionally effected such that the focusing actuator 9 moves the objective lens 6 in a direction where a focal point is to be adjusted while the tracking actuator 10 moves in a direction of tracking, the objective lens 6, focusing actuator 9, optical path converting prism mirror 5, and a trackinhg movable part casing 12 for supporting the foregoing members, all those members being integrally united in a head casing 11.
The conventional optical head however requires a complicated precission mechanism because in the arrangement described above the tracking movable part casting 12 must be supported linearly movably only in a direction of the light beam emitted from the optical source 1 by a supporting members 13. Such conventional arrangement also requires the same mechanism because the objective lens 6 must be moved accurately linearly perpendicularly to the direction of the movement of the movable part casing 12 by a supporting member 14, the movable part casing moving in the direction of the optical path extending from the optical source 1. This conventional head has another problem in that it is difficult to assure accuracy in assembly and adjustment of the device because the directions of driving of the actuators 9, 10 are different, i.e. perpendicular to each other, and the supporting members 14, 13 are intervened respectively between the focusing actuator 9 and the objective lens 6, and between the tracking actuator 10 and the tracking movable part casing 12. Such conventional head furthermore suffers from a problem that the higher order resonance of the mechanism in the direction of the tracking is liable to occur in a low frequency region owing to the supporting member 14 because the objective lens 6 is supported through the movable part casing 12 and the supporting members 13, 14.
In view of the drawbacks of the conventional optical head, it is an object of the present invention to provide an improved optical head capable of avoiding the aforementioned problems and of restricting resonance frequencies to a high frequency region with a simplified structure.